Electrical interconnect structure and method

ABSTRACT

An electrical structure and method of forming. The electrical structure includes a first substrate comprising a first electrically conductive pad, a second substrate comprising a second electrically conductive pad, and an interconnect structure electrically and mechanically connecting the first electrically conductive pad to the second electrically conductive pad. The interconnect structure comprises a non-solder metallic core structure, a first solder structure, and a second solder structure. The first solder structure electrically and mechanically connects a first portion of the non-solder metallic core structure to the first electrically conductive pad. The second solder structure electrically and mechanically connects a second portion of the non-solder metallic core structure to the second electrically conductive pad.

FIELD OF THE INVENTION

The present invention relates to an electrical interconnect structureand associated method for forming an electrical interconnect structure.

BACKGROUND OF THE INVENTION

Connections between structures are typically unreliable and subject tofailure. Accordingly, there exists a need in the art to overcome atleast one of the deficiencies and limitations described herein above.

SUMMARY OF THE INVENTION

The present invention provides an electrical structure comprising:

a first substrate comprising a first electrically conductive pad;

a second substrate comprising a second electrically conductive pad; and

an interconnect structure electrically and mechanically connecting saidfirst electrically conductive pad to said second electrically conductivepad, wherein said interconnect structure comprises a non-solder metalliccore structure, a first solder structure in direct mechanical contactwith a first portion of said non-solder metallic core structure, and asecond solder structure in direct mechanical contact with a secondportion of said non-solder metallic core structure, wherein said firstsolder structure electrically and mechanically connects said firstportion of said non-solder metallic core structure to said firstelectrically conductive pad, and wherein said second solder structureelectrically and mechanically connects said second portion of saidnon-solder metallic core structure to said second electricallyconductive pad.

The present invention provides an electrical structure comprising:

a first substrate comprising a first electrically conductive pad;

a second substrate comprising a second electrically conductive pad; and

an interconnect structure electrically and mechanically connecting saidfirst electrically conductive pad to said second electrically conductivepad, wherein said interconnect structure comprises a non-solder metalliccore structure and a layer of solder covering an entire exterior surfaceof said non-solder metallic core structure, wherein said entire exteriorsurface completely surrounds said first metallic structure, wherein saidlayer of solder is in direct electrical and mechanical contact with saidentire surface of said non-solder metallic core structure, and whereinsaid layer of solder electrically and mechanically connects saidnon-solder metallic core structure to said first electrically conductivepad and said second electrically conductive pad.

The present invention provides a method for forming an electricalstructure comprising:

providing a first substrate comprising a first electrically conductivepad, a second substrate comprising a second electrically conductive pad,and a transfer film comprising a non-solder metallic core structure,wherein said non-solder metallic core structure comprises a cylindricalshape;

forming a first solder structure on said first electrically conductivepad;

first positioning after said forming said first solder structure, saidtransfer film such that a first side of said non-solder metallic corestructure is in contact with said first solder structure;

first heating after said first positioning, said non-solder metalliccore structure to a temperature sufficient to cause said first solderstructure to melt and form an electrical and mechanical connectionbetween said first side of said non-solder metallic core structure andsaid first electrically conductive pad;

removing after said first heating, said transfer film from saidnon-solder metallic core structure;

forming a second solder structure on said second electrically conductivepad;

second positioning, after said forming said second solder structure,said first substrate comprising said non-solder metallic core structuresuch that a second side of said non-solder metallic core structure is incontact said second solder structure; and

second heating after said second positioning, said non-solder metalliccore structure to a temperature sufficient to cause said second solderstructure solder to melt and form an electrical and mechanicalconnection between said second side of said non-solder metallic corestructure and said second electrically conductive pad resulting in anelectrical and mechanical connection between said first electricallyconductive pad and said second electrically conductive pad.

The present invention provides a method for forming an electricalstructure comprising:

providing a first substrate comprising a first electrically conductivepad, a second substrate comprising a second electrically conductive pad,a first transfer substrate comprising a first cavity, and a non-soldermetallic core structure comprising a spherical shape, wherein saidnon-solder metallic core structure comprises a diameter that is lessthan a diameter of said first cavity;

forming a first solder structure on said first electrically conductivepad;

dispensing said non-solder metallic core structure into said firstcavity within said first transfer substrate;

first positioning after said dispensing, said first transfer substratesuch that a first section of a surface of said non-solder metallic corestructure is in contact with said first solder structure;

first heating after said first positioning, said non-solder metalliccore structure to a temperature sufficient to cause said first solderstructure to melt and form an electrical and mechanical connectionbetween said first section of said surface of said non-solder metalliccore structure and said first electrically conductive pad;

removing after said first heating, said first transfer substrate fromsaid non-solder metallic core structure;

forming a second solder structure on said second electrically conductivepad;

second positioning said first substrate comprising said non-soldermetallic core structure such that a second section of said surface ofsaid non-solder metallic core structure is in contact with said secondsolder structure; and

second heating after said second positioning, said non-solder metalliccore structure to a temperature sufficient to cause said second solderstructure solder to melt and form an electrical and mechanicalconnection between said second section of said surface of saidnon-solder metallic core structure and said second electricallyconductive pad resulting in an electrical and mechanical connectionbetween said first electrically conductive pad and said secondelectrically conductive pad.

The present invention provides a method for forming an electricalstructure comprising:

providing a first substrate comprising a first electrically conductivepad, a second substrate comprising a second electrically conductive pad,a first transfer substrate comprising a first cavity, a first non-soldermetallic core structure comprising a spherical shape, and a secondnon-solder metallic core structure comprising a spherical shape, whereinsaid first non-solder metallic core structure comprises a diameter thatis less than a diameter of said first cavity, and wherein said secondnon-solder metallic core structure comprises a diameter that is lessthan a diameter of said first cavity;

forming a first solder structure on said first electrically conductivepad;

first dispensing said first non-solder metallic core structure into saidfirst cavity within said first transfer substrate;

first positioning after said first dispensing, said first transfersubstrate such that a first section of a surface of said firstnon-solder metallic core structure is in contact with said first solderstructure;

first heating after said first positioning, said first non-soldermetallic core structure to a temperature sufficient to cause said firstsolder structure to melt and form an electrical and mechanicalconnection between said first section of said surface of said firstnon-solder metallic core structure and said first electricallyconductive pad;

removing after said first heating, said first transfer substrate fromsaid non-solder metallic core structure;

applying a first underfill encapsulant layer to said first substrate;

forming a second solder structure on a second section of said surface ofsaid first non-solder metallic core structure;

second dispensing said second non-solder metallic core structure intosaid first cavity within said first transfer substrate;

second positioning after said second dispensing, said first transfersubstrate such that a first section of a surface of said secondnon-solder metallic core structure is in contact with said second solderstructure;

second heating after said second positioning, said second non-soldermetallic core structure to a temperature sufficient to cause said secondsolder structure to melt and form an electrical and mechanicalconnection between said second section of said surface of said firstnon-solder metallic core structure and said first section of saidsurface of said second non-solder metallic core structure;

removing after said heating said first portion of said second non-soldermetallic core structure, said first transfer substrate from said secondnon-solder metallic core structure;

forming a third solder structure on said second electrically conductivepad;

third positioning said first substrate comprising said first non-soldermetallic core and said second non-solder metallic core structure suchthat a second section of said surface of said second non-solder metalliccore structure is in contact with said second solder structure; and

third heating after said third positioning, said second non-soldermetallic core structure to a temperature sufficient to cause said thirdsolder structure solder to melt and form an electrical and mechanicalconnection between said second section of said surface of said secondnon-solder metallic core structure and said second electricallyconductive pad resulting in an electrical and mechanical connectionbetween said first electrically conductive pad and said secondelectrically conductive pad.

The present invention provides a method for forming an electricalstructure comprising:

providing a first substrate comprising a first electrically conductivepad and a second electrically conductive pad, a second substratecomprising third electrically conductive pad and a fourth electricallyconductive pad, a first transfer substrate comprising a first cavity anda second cavity, and a non-solder metallic core structure comprising aspherical shape, wherein said non-solder metallic core structurecomprises a diameter that is less than a diameter of said first cavity;

forming a first solder structure on said first electrically conductivepad;

forming a second solder structure on said second electrically conductivepad;

covering said second cavity with a film having an opening correspondingto said first cavity;

dispensing said non-solder metallic core structure into said firstcavity within said first transfer substrate;

first positioning said first transfer substrate such that a firstsection of a surface of said non-solder metallic core structure is incontact with said first solder structure and said second cavity isaligned with said second solder structure;

first heating said non-solder metallic core structure to a temperaturesufficient to cause said first solder structure to melt and form anelectrical and mechanical connection between said first section of saidsurface of said non-solder metallic core structure and said firstelectrically conductive pad;

removing said first transfer substrate from said non-solder metalliccore structure;

forming a third solder structure on said third electrically conductivepad;

forming a fourth solder structure on said fourth electrically conductivepad;

second positioning said first substrate comprising said non-soldermetallic core structure such that a second section of said surface ofsaid non-solder metallic core structure is in contact with said thirdsolder structure and said second solder structure is in contact withsaid fourth solder structure;

second heating said non-solder metallic core structure to a temperaturesufficient to cause said third solder structure solder to melt and forman electrical and mechanical connection between said second section ofsaid surface of said non-solder metallic core structure and said thirdelectrically conductive pad resulting in an electrical and mechanicalconnection between said first electrically conductive pad and said thirdelectrically conductive pad; and

third heating said second solder structure and said fourth solderstructure to a temperature sufficient to cause said second solderstructure and said fourth solder structure to melt and form anelectrical and mechanical connection between said second solderstructure and said fourth solder structure resulting in an electricaland mechanical connection between said second electrically conductivepad and said fourth electrically conductive pad, wherein said secondheating and said third heating are performed simultaneously.

The present invention advantageously provides a simple structure andassociated method for forming connections between structures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross sectional view of a first electricalstructure, in accordance with embodiments of the present invention

FIG. 2 depicts a first alternative to FIG. 1 illustrating a crosssectional view of a second electrical structure, in accordance withembodiments of the present invention.

FIG. 3 depicts a first alternative to FIG. 2 illustrating a crosssectional view of a third electrical structure, in accordance withembodiments of the present invention.

FIG. 4 depicts a first alternative to FIG. 3 illustrating a crosssectional view of a fourth electrical structure, in accordance withembodiments of the present invention.

FIG. 5 illustrates a cross sectional view of a fifth electricalstructure, in accordance with embodiments of the present invention.

FIG. 6 depicts a second alternative to FIG. 2 illustrating a crosssectional view of a sixth electrical structure, in accordance withembodiments of the present invention.

FIG. 7 depicts a second alternative to FIG. 1 illustrating a crosssectional view of an seventh electrical structure, in accordance withembodiments of the present invention.

FIG. 8 depicts a second alternative to FIG. 3 illustrating a crosssectional view of a eighth electrical structure, in accordance withembodiments of the present invention.

FIGS. 9A-9G illustrate a process for generating the electrical structureof FIG. 1, in accordance with embodiments of the present invention.

FIGS. 10A-10I illustrate a process for generating the electricalstructures of FIG. 2, FIG. 3, and FIG. 5, in accordance with embodimentsof the present invention.

FIGS. 11A-11F illustrate a process for generating the electricalstructure of FIG. 4, in accordance with embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a cross sectional view of an electrical structure 2a, in accordance with embodiments of the present invention. Electricalstructure 2 a comprises a substrate 1, a substrate 4, and a plurality ofinterconnect structures 5 a. Substrate 1 comprises a plurality ofelectrically conductive pads 10. Each pad of electrically conductivepads 10 may be connected to wires or electrical components withinsubstrate 1. Substrate 4 comprises a plurality of electricallyconductive pads 12. Each pad of electrically conductive pads 12 may beconnected to wires or electrical components within substrate 4.Substrate 1 may comprise, inter alia, a semiconductor device (e.g., anintegrated circuit chip, a semiconductor wafer, etc), a chip carrier(organic or inorganic), a printed circuit board, etc. Substrate 4 maycomprise, inter alia, a semiconductor device (e.g., an integratedcircuit chip, a semiconductor wafer, etc), a chip carrier (organic orinorganic), a printed circuit board, etc. Each interconnect structure 5a comprises a non-solder metallic (i.e., does not comprise any soldermaterial) core structure 14 and a solder structure 6 a. Solder structure6 a comprises solder. Solder is defined herein as a metal alloycomprising a low melting point (i.e., about 100 degrees Celsius to about340 degrees Celsius) that is used to join metallic surfaces togetherwithout melting the metallic surfaces. Solder structure 6 a comprises alayer of solder that completely surrounds non-solder metallic corestructure 14. Alternatively (i.e., instead of a layer of solder thatcompletely surrounds non-solder metallic core structure 14), solderstructure 6 a could comprise a first portion of solder 9 a attached to atop side 14 a of non-solder metallic core structure 14 and a secondportion of solder 9 b attached to a bottom side 14 b of non-soldermetallic core structure 14. Each non-solder metallic core structure 14may comprise any conductive metallic material that does not comprisesolder including, inter alia, copper, gold, nickel, etc. Eachinterconnect structure 5 a electrically and mechanically connects anelectrically conductive pad 10 to an electrically conductive pad 12.Non-solder metallic core structure 14 comprises a cylindrical shape.Solder structure 6 a may comprise any solder material suitable for flipchip interconnections including, inter alia, an alloy of tin such asSnCu, SnAgCu, SnPb, etc.

FIG. 2 depicts a first alternative to FIG. 1 illustrating across-sectional view of an electrical structure 2 b, in accordance withembodiments of the present invention. Electrical structure 2 b comprisessubstrate 1, substrate 4, and a plurality of interconnect structures 5b. In contrast with electrical structure 2 a of FIG. 1, electricalstructure 2 b of FIG. 2 comprises a plurality of interconnect structures5 b. Each of interconnect structures 5 b comprises a sphericalnon-solder (i.e., does not comprise any solder material) metallic corestructure 17 and a solder structure 6 b. Each solder structure 6 bcomprises a layer of solder that completely surrounds an associatednon-solder metallic core structure 17. Additionally, each ofinterconnect structures 5 b may comprise an additional solder structure6 d. Each solder structure 6 b electrically and mechanically connectsthe associated non-solder metallic core structure 17 to an associatedelectrically conductive pad 10. Each solder structure 6 d electricallyand mechanically connects the associated non-solder metallic corestructure 17 (i.e., thru solder structure 6 b) to an associatedelectrically conductive pad 12. The aforementioned connections result ineach interconnect structure 5 b electrically and mechanically connectingan electrically conductive pad 10 to an associated electricallyconductive pad 12. Optionally, two different types of solder materialsmay be used for solder structure 6 b and solder structure 6 d. Forexample, solder structure 6 b may comprise an AuSn solder material andsolder structure 6 d may comprise a solder material such as, inter alia,SnAg, SnCu, SnAgCu, SnBi, etc. For first level area array interconnects,each non-solder metallic core structure 17 may comprise a diameter ofabout 25 microns to about 150 microns. For second level area arrayinterconnects (e.g., a ball grid array (BGA)), each non-solder metalliccore structure 17 may comprise a diameter of about 0.2 mm to about 1.5mm. Each non-solder metallic core structure 17 may comprise a core ofany conductive metallic material that does not comprise solderincluding, inter alia, copper, gold, nickel, etc. Additionally, eachnon-solder metallic core structure 17 may comprise an additionallayer(s) of non-solder metallic materials (i.e., different from amaterial comprised by non-solder metallic core structure 17) surrounding(e.g., see layer 19 in FIG. 3, infra) non-solder metallic core structure17. The additional layer(s) may comprise any conductive metallicmaterial including, inter alia, nickel, gold, tin, etc.

FIG. 3 depicts a first alternative to FIG. 2 illustrating a crosssectional view of an electrical structure 2 c, in accordance withembodiments of the present invention. Electrical structure 2 c comprisessubstrate 1, substrate 4, and a plurality of interconnect structures 5c. In contrast with electrical structure 2 b of FIG. 2, electricalstructure 2 c of FIG. 3 comprises a plurality of interconnect structures5 c. Each of interconnect structures 5 c comprises a non-solder metalliccore structure 17, a solder structure 6 c, and a solder structure 6 d.Each solder structure 6 c electrically and mechanically connects anassociated non-solder metallic core structure 17 to an associatedelectrically conductive pad 10. Each solder structure 6 d electricallyand mechanically connects an associated non-solder metallic corestructure 17 to an associated electrically conductive pad 12. Theaforementioned connections result in each interconnect structure 5 celectrically and mechanically connecting an electrically conductive pad10 to an associated electrically conductive pad 12. Optionally, twodifferent types of solder materials may be used for solder structure 6 cand solder structure 6 d. For example, solder structure 6 c may comprisean AuSn solder material and solder structure 6 d may comprise a soldermaterial such as, inter alia, SnAg, SnCu, SnAgCu, SnBi, etc. Eachnon-solder metallic core structure 17 may comprise a core of anyconductive metallic material that does not comprise solder including,inter alia, copper, gold, nickel, etc. Additionally, each non-soldermetallic core structure 17 may comprise an additional layer(s) 19 ofnon-solder metallic materials (i.e., different from a material comprisedby non-solder metallic core structure 17) surrounding non-soldermetallic core structure 17. Additional layer(s) 19 may comprise anyconductive metallic material including, inter alia, nickel, gold, tin,etc.

FIG. 4 depicts a first alternative to FIG. 3 illustrating a crosssectional view of an electrical structure 2 d, in accordance withembodiments of the present invention. Electrical structure 2 d comprisessubstrate 1, substrate 4, and a plurality of interconnect structures 5d. In contrast with electrical structure 2 c of FIG. 3, electricalstructure 2 d of FIG. 4 comprises a plurality of interconnect structures5 d. Each of interconnect structures 5 d comprises a non-solder metalliccore structure 17 a, a non-solder metallic core structure 17 b, a solderstructure 6 c, a solder structure 6 d, a solder structure 6 e.Additionally (i.e., optionally), electrical structure 2 d comprises anunderfill encapsulant layer 25 a and an underfill encapsulant layer 25b. Each solder structure 6 e electrically and mechanically connects anon-solder metallic core structure 17 a to an associated a non-soldermetallic core structure 17 b. Each solder structure 6 c electrically andmechanically connects a non-solder metallic core structure 17 a to anassociated electrically conductive pad 10. Each solder structure 6 delectrically and mechanically connects a non-solder metallic corestructure 17 b to an associated electrically conductive pad 12. Theaforementioned connections result in each interconnect structure 5 delectrically and mechanically connecting an electrically conductive pad10 to an associated electrically conductive pad 12. Optionally, threedifferent types of solder materials may be used for solder structure 6c, solder structure 6 d, and solder structure 6 e. For example, solderstructure 6 c may comprise an AuSn solder material, solder structure 6 dmay comprise a solder material such as, inter alia, SnAg, SnCu, etc, andsolder structure 6 e may comprise a solder material such as, inter alia,SnAgCu, SnBi, etc. Each non-solder metallic core structure 17 a and 17 bmay comprise a core of any conductive metallic material that does notcomprise solder including, inter alia, copper, gold, nickel, etc.Non-solder metallic core structure 17 a may comprise a first material(e.g., copper) and non-solder metallic core structure 17 b may comprisea second material (e.g., gold). Additionally, each non-solder metalliccore structure 17 a and 17 b may comprise an additional layer(s) 19 ofmetallic materials (i.e., different from a material comprised bynon-solder metallic core structure 17 a and 17 b) surrounding non-soldermetallic core structure 17 a and 17 b. Additional layer(s) 19 maycomprise any conductive metallic material including, inter alia, nickel,gold, tin, etc. Additionally, non-solder metallic core structure 17 amay comprise a layer(s) 19 comprising a different material from alayer(s) 19 on non-solder metallic core structure 17 b. Underfillencapsulant layer 25 a surrounds non-solder metallic core structures 17a and is in contact with substrate 1. Underfill encapsulant layer 25 bsurrounds non-solder metallic core structures 17 b and is in contactwith substrate 4. Underfill encapsulant layer 25 a is in contact withunderfill encapsulant layer 25 b. Underfill encapsulant layer 25 a maycomprise a first material (e.g., a highly filled silica-epoxy compositeadhesive) and underfill encapsulant layer 25 b may comprise a second anddifferent material (e.g., a lightly filled silica-epoxy compositeadhesive). Underfill encapsulant layer 25 a may comprise a firstcoefficient of thermal expansion (e.g., comprising a range of about 5-15ppm/C) that is different (e.g., lower) from a second coefficient ofthermal expansion (e.g., comprising a range of about 15.1-40 ppm/C)comprised by encapsulant layer 25 b. Underfill encapsulent layer 25 amay additionally comprise a filler 25 c dispersed throughout.

FIG. 5 illustrates a cross sectional view of an electrical structure 2e, in accordance with embodiments of the present invention. Electricalstructure 2 e in FIG. 5 is a combination of electrical structures 2 band 2 c, of FIGS. 2-3. In addition to electrical structures 2 b and 2 c,of FIGS. 2-3, electrical structure 2 e in FIG. 5 comprisesinterconnection structures 29 (i.e., comprising solder) electrically andmechanically connecting some of electrically conductive pads 10 toassociated electrically conductive pads 12. Therefore, electricalstructure 2 e uses a combination of interconnect structures 5 b, 5 c,and 29 to electrically and mechanically connect electrically conductivepads 10 to associated electrically conductive pads 12. Note that anycombination and any configuration of interconnect structures 5 b, 5 c,and 29 may be used to electrically and mechanically connect electricallyconductive pads 10 to associated electrically conductive pads 12. Forexample, electrical structure 2 e may comprise only interconnectstructures 5 c and 29 to electrically and mechanically connectelectrically conductive pads 10 to associated electrically conductivepads 12. There may be any number or ratio of interconnect structures 5b, 5 c, and 29 arranged in any pattern (e.g., interconnect structures 5b and 29: may be placed such that they are in alternating positions, maybe placed in random positions, may be placed such that there is oneinterconnect structure 5 b for every three interconnect structures 29,may be placed such that interconnect structures 5 b provide power andground connections only and interconnect structures 29 are placed forsignal interconnects only, etc). Additionally, electrical structure 2 emay comprise an underfill encapsulant layer 31 between substrate 1 andsubstrate 4.

FIG. 6 depicts a second alternative to FIG. 2 illustrating a crosssectional view of an electrical structure 2 f, in accordance withembodiments of the present invention. In contrast with electricalstructure 2 b of FIG. 2, electrical structure 2 f of FIG. 6 comprises anunderfill encapsulant layer 32 a between substrate 1 and substrate 4. Inthe case in which substrate 1 is a semiconductor device or a siliconwafer, underfill encapsulant layer 32 a may alternately comprise anunderfill layer applied prior to chip joining or applied on the siliconwafer over the interconnect structures 5 b. Such an underfill layer isdefined as a wafer-level underfill.

FIG. 7 depicts a second alternative to FIG. 1 illustrating a crosssectional view of an electrical structure 2 g, in accordance withembodiments of the present invention. In contrast with electricalstructure 2 a of FIG. 1, electrical structure 2 g of FIG. 7 comprises anunderfill encapsulant layer 32 b between substrate 1 and substrate 4. Inthe case in which substrate 1 is a semiconductor device or a siliconwafer, underfill encapsulant layer 32 b may alternately comprise anunderfill layer applied prior to chip joining or applied on the siliconwafer over the interconnect structures 5 a. Such an underfill layer isdefined as a wafer-level underfill

FIG. 8 depicts a second alternative to FIG. 3 illustrating a crosssectional view of an electrical structure 2 h, in accordance withembodiments of the present invention. In contrast with electricalstructure 2 c of FIG. 3, electrical structure 2 h of FIG. 8 comprises anunderfill encapsulant layer 32 c between substrate 1 and substrate 4. Inthe case in which substrate 1 is a semiconductor device or a siliconwafer, underfill encapsulant layer 32 c may alternately comprise anunderfill layer applied prior to chip joining or applied on the siliconwafer over the interconnect structures 5 c. Such an underfill layer isdefined as a wafer-level underfill.

FIGS. 9A-9G illustrate a process for generating electrical structure 2 aof FIG. 1, in accordance with embodiments of the present invention.

FIG. 9A illustrates a cross sectional view of a non-solder metalliclayer 37 formed over an insulator layer 35, in accordance withembodiments of the present invention. Non-solder metallic layer 37 maycomprise any non-solder metallic material such as, inter alia, copper,gold, nickel, etc. Insulator layer 35 may comprise any insulatormaterial such as, inter alia, a polymer film (e.g., polyimide), etc.

FIG. 9B illustrates a cross sectional view of the structure of FIG. 9Aafter non-solder metallic interconnect structures 14 have been formed inorder to form structure 35 a, in accordance with embodiments of thepresent invention. Non-solder metallic interconnect structures 14 may beformed by subtractively etching portions of non-solder metallic layer 37(i.e., of FIG. 1) in order to form non-solder metallic interconnectstructures 14. Non-solder metallic interconnect structures 14 maycomprise various widths, heights, and height-to-width aspect ratios. Asubtractive etching process comprises:

-   1. Applying and patterning a protective photo resist layer-   2. Using chemical solutions to etch or dissolve unprotected regions    of copper.-   3. Stripping off the protective photo resist layer.

Each of non-solder metallic interconnect structures 14 may comprise awidth of about 10 microns to about 100 microns and comprise aheight-to-width aspect ratio of about 1:1 to about 5:1.

FIG. 9C illustrates a cross sectional view of substrate 1 of FIG. 1after first portions of solder 9 a (i.e., solder structures) have beenformed thereby forming a structure 35 b, in accordance with embodimentsof the present invention. For example, substrate 1 may comprise asilicon device wafer that is prepared with electrically conductiveinterconnect pads (e.g., see pads 10 of FIG. 1). Solder is applied tothe pads in order to form first portions of solder 9 a. Any method maybe used to apply the solder to the electrically conductive interconnectpads, including, inter alia, applying solder as an injection moldedsolder.

FIG. 9D illustrates a cross sectional view of structure 35 a of FIG. 9Bof FIG. 1 aligned with structure 35 b of FIG. 9C, in accordance withembodiments of the present invention. Non-solder metallic interconnectstructures 14 are aligned to associated first portions of solder 9 a.The alignment process may comprise using commercially available bondingtools that use optical sensing of fiducials on substrate 1 and insulatorlayer 35.

FIG. 9E illustrates a cross sectional view of structure 35 c formedafter the alignment process described with respect to FIG. 9D, inaccordance with embodiments of the present invention. In FIG. 9E, atransfer process has been performed by heating the aligned assembly ofFIG. 9D to a temperature above a melting point (i.e., with assistance ofa fluxing agent or a fluxing atmosphere) of the solder used to formfirst portions of solder 9 a. Optionally, the transfer process may beassisted by a laser release process applied through a backside 21 ofinsulator layer 35. Light energy generated by a laser is absorbed byinsulator layer 35 at an interface 23 to non-solder metallicinterconnect structures 14 causes adhesion (i.e., at interface 23) to bedegraded hereby releasing non-solder metallic interconnect structures 14from insulator layer 35. Alternatively, an adhesive (i.e., at interface23) may be degraded and release non-solder metallic interconnectstructures 14 from insulator layer 35 during the solder melting processdescribed, supra.

FIG. 9F illustrates a cross sectional view of a process for aligningstructure 35 c of FIG. 9E with a structure 35 d, in accordance withembodiments of the present invention. Structure 35 d comprises asubstrate 4 comprising formed solder structures 9 b (i.e., formed by asimilar process to the process performed with respect to FIG. 9C).

FIG. 9G illustrates a completed electrical structure 35 e similar toelectrical structure 2 a of FIG. 1, in accordance with embodiments ofthe present invention. An assembly of substrate 1 to substrate 4 throughnon-solder metallic interconnect structures 14, solder structures 9 a,and solder structures 9 b is carried out by raising a temperature ofnon-solder metallic interconnect structures 14 above a meltingtemperature of solder structures 9 b with the assistance of a fluxingagent or fluxing atmosphere. Optionally, non-solder metallicinterconnect structures 14, solder structures 9 a, and solder structures9 b may be encapsulated with polymeric material by capillary underfillfollowing the joining of substrate 1 to substrate 4. Alternatively, anunderfill encapsulant may be applied at wafer-level or on singulateddevices prior to the joining of substrate 1 to substrate 4.

FIGS. 10A-10I illustrate a process for generating electrical structure 2b of FIG. 2, electrical structure 2 c of FIG. 3, and electricalstructure 2 e of FIG. 5, in accordance with embodiments of the presentinvention. Note that although FIGS. 10A-10I illustrate a process forapplying solder as an injection molded solder, any solder applyingprocess may be used.

FIG. 10A illustrates a cross sectional view of a structure 39 acomprising a filled glass or silicon mold 40 positioned over substrate 1(i.e., from FIGS. 2 and 3), in accordance with embodiments of thepresent invention. Glass or silicon mold 40 is filled with solder thatwhen released from glass mold will become solder structures 6 b of FIG.2, 6 c of FIG. 3, and 6 b of FIG. 5. The solder may comprise any soldersuitable for flip chip interconnects including, inter alia, an alloy oftin such as, inter alia, AuSn, SnCu, SnAgCu, etc. The solder maycomprise a high melting point so that solder structures 6 b, 6 c willnot melt during a subsequent step.

FIG. 10B illustrates a cross sectional view of a structure of 39 bformed from structure 39 a of FIG. 10A, in accordance with embodimentsof the present invention. In FIG. 10B, the solder has been released fromglass or silicon mold 40 to form solder structures 6 c attached toelectrically conductive pads 10 on substrate 1.

FIG. 10C illustrates a cross sectional view of a transfer substrate 43comprising a plurality of non-solder metallic core structures 17, inaccordance with embodiments of the present invention. Non-soldermetallic core structures 17 are positioned in cavities 43 a withintransfer substrate 43. Each of cavities 43 a comprises similardimensions as non-solder metallic core structures 17 with cavitypositions corresponding to positions of associated solder structures 6 con electrically conductive pads 10. Transfer substrate 43 may comprise,inter alia, glass, silicon, or any material used for injection moldedsolder molds, etc. Non-solder metallic core structures 17 may bedispensed into cavities 43 a as a slurry in a solvent such as, interalia, water alcohol (e.g., isopropanol), etc. The solvent may comprisean appropriate amount of flux to assist in the wetting of solderstructures 6 c to non-solder metallic core structures 17. In a case inwhich non-solder metallic core structures 17 are coated with gold, fluxis not necessary. Optionally, the solvent may additionally comprise asmall amount of thermally degradable polymeric adhesive to aid inretaining non-solder metallic core structures 17 in cavities 43 a.Cavities 43 a are fabricated to a size that will only cause onenon-solder metallic core structure 17 to fall into it during adispensing of non-solder metallic core structures 17.

FIG. 10D illustrates a cross sectional view of transfer substrate 43 ofFIG. 10C comprising a selected plurality of non-solder metallic corestructures 17, in accordance with embodiments of the present invention.As an optional feature of the process, transfer substrate 43 may becovered with a polymeric film (i.e., not shown) with through-holesmatching some pre-determined fraction of cavities 43 a. Thepre-determined fraction of cavities 43 a covered by the polymeric filmwill be prevented from receiving non-solder metallic core structures 17.The pre-determined fraction of cavities 43 a allows a packaging designengineer to selectively place non-solder metallic core structures 17.Additionally, solder interconnects 29 may be selectively placed in someof cavities 43 a (i.e., instead of select non-solder metallic corestructures 17) for placement on substrate 1. In this option, transfersubstrate 43 may be covered with a second polymeric film (i.e., notshown) with through-holes matching the remaining cavities 43 a. Thecavities 43 a covered by the polymeric film will be prevented fromreceiving solder interconnects 29.

FIG. 10E illustrates a cross sectional view of substrate 1 of FIG. 10Bpositioned over transfer substrate 43 comprising non-solder metalliccore structures 17, in accordance with embodiments of the presentinvention. Substrate 1 of FIG. 10B is positioned over transfer substrate43 comprising non-solder metallic core structures 17 in order totransfer non-solder metallic core structures 17 to substrate 1.

FIG. 10F illustrates a cross sectional view of substrate 1 afternon-solder metallic core structures 17 have been released from transfersubstrate 43 and connected to solder structures 6 b, in accordance withembodiments of the present invention. In FIG. 10F, solder structures 6 bcompletely surround non-solder metallic core structures 17.

FIG. 10G depicts an alternative to FIG. 10F illustrating a crosssectional view of a structure 39 c comprising substrate 1 afternon-solder metallic core structures 17 have been released from transfersubstrate 43 and connected to solder structures 6 c, in accordance withembodiments of the present invention. In FIG. 10G, solder structures 6 cpartially surround non-solder metallic core structures 17.

FIG. 10H illustrates a cross sectional view of substrate 1 positionedover substrate 4, in accordance with embodiments of the presentinvention. Substrate 1 is connected to substrate 4 in order to formelectrical structure 2 b of FIG. 2.

FIG. 10I illustrates an alternative cross sectional view of substrate 1positioned over substrate 4, in accordance with embodiments of thepresent invention. In the case in which the option of FIG. 10D is used(i.e., comprising solder interconnect structures 29), the positioning(not shown) is done similarly as in FIG. 10I. Substrate 1 is connectedto substrate 4 in order to form electrical structure 2 c of FIG. 3.

FIGS. 11A-11F illustrate a process for generating electrical structure 2d of FIG. 4, in accordance with embodiments of the present invention.

FIG. 11A illustrates structure 39 c of FIG. 10G comprising an underfilllayer 25 a, in accordance with embodiments of the present invention.Structure 39 c in FIG. 11A has been formed by the process stepsdescribed with reference to FIGS. 10A-10E. Underfill layer 25 a maycomprise a filler 25 c to create a low coefficient of thermal expansion(CTE). Underfill layer 25 a may comprise a coefficient of thermalexpansion (CTE) similar to that of substrate 1.

FIG. 11B illustrates structure 39 c comprising a glass or silicon mold40 b positioned over non-solder metallic core structures 17 a, inaccordance with embodiments of the present invention. Glass or siliconmold 40 b is filled with solder that when released from mold 40 b willbecome solder structures 6 e of FIG. 4. The solder may comprise anysolder suitable for flip chip interconnects including, inter alia, analloy of tin such as, inter alia, AuSn, SnCu, SnAgCu, etc. The soldermay comprise a high melting point so that solder structures 6 e will notmelt during a subsequent step.

FIG. 11C illustrates a cross sectional view of structure of 39 ccomprising solder structures 6 e attached to non-solder metallic corestructures 17 a, in accordance with embodiments of the presentinvention. In FIG. 11C, the solder has been released from glass orsilicon mold 40 b to form solder structures 6 e attached to non-soldermetallic core structures 17 a.

FIG. 11D illustrates a cross sectional view of structure 39 c of FIG.11C positioned over a transfer substrate 43 comprising non-soldermetallic core structures 17 b, in accordance with embodiments of thepresent invention. Structure 39 c of FIG. 11C is positioned overtransfer substrate 43 comprising non-solder metallic core structures 17b in order to transfer and connect non-solder metallic core structures17 b to non-solder metallic core structures 17 a.

FIG. 11E illustrates a cross sectional view of structure 39 c of FIG.11D after non-solder metallic core structures 17 b have been connectedto non-solder metallic core structures 17 a, in accordance withembodiments of the present invention.

FIG. 11F illustrates a cross sectional view of structure 39 c of FIG.11E comprising an underfill layer 25 b applied over underfill layer 25a, in accordance with embodiments of the present invention. Afterunderfill layer 25 b is applied over underfill layer 25 a, substrate 1is connected to substrate 4 in order to form electrical structure 2 d ofFIG. 4.

While embodiments of the present invention have been described hereinfor purposes of illustration, many modifications and changes will becomeapparent to those skilled in the art. Accordingly, the appended claimsare intended to encompass all such modifications and changes as fallwithin the true spirit and scope of this invention.

1. An electrical structure comprising: a first substrate comprising afirst electrically conductive pad; a second substrate comprising asecond electrically conductive pad; and an interconnect structureelectrically and mechanically connecting said first electricallyconductive pad to said second electrically conductive pad, wherein saidinterconnect structure comprises a non-solder metallic core structure, afirst solder structure in direct mechanical contact with a first portionof said non-solder metallic core structure, and a second solderstructure in direct mechanical contact with a second portion of saidnon-solder metallic core structure, wherein said first solder structureelectrically and mechanically connects said first portion of saidnon-solder metallic core structure to said first electrically conductivepad, and wherein said second solder structure electrically andmechanically connects said second portion of said non-solder metalliccore structure to said second electrically conductive pad.
 2. Theelectrical structure of claim 1, wherein said non-solder metallic corestructure comprises a cylindrical shape.
 3. The electrical structure ofclaim 1, wherein said non-solder metallic core structure comprises aspherical shape.
 4. The electrical structure of claim 1, wherein saidnon-solder metallic core structure comprises a metallic materialselected from the group consisting of copper, nickel, and gold.
 5. Theelectrical structure of claim 1, wherein said non-solder metallic corestructure comprises a first metallic structure and a second metallicstructure covering and in direct mechanical contact with an entireexterior surface of said first metallic structure, wherein said entireexterior surface completely surrounds said first metallic structure, andwherein said first metallic structure consists of a first metallicmaterial, and wherein said second metallic structure consists of asecond metallic material that differs from the first metallic material.6. The electrical structure of claim 1, wherein said interconnectstructure comprises a third solder structure, wherein said non-soldermetallic core structure comprises a first non-solder metallic corecomprising a spherical shape and a second non-solder metallic corecomprising said spherical shape, wherein said third solder structureelectrically and mechanically attaches said first non-solder metalliccore to said second non-solder metallic core, wherein said first portionof said non-solder metallic core structure is located on said firstnon-solder metallic core, and wherein said second portion of saidnon-solder metallic core structure is located on said non-soldermetallic core.
 7. The electrical structure of claim 6, wherein saidfirst solder structure comprises a first solder material, wherein saidsecond solder structure comprises a second solder material, and whereinsaid first solder material is different from said second soldermaterial.
 8. The electrical structure of claim 7, wherein said thirdsolder structure comprises a third solder material, and wherein saidthird solder material is different from said first solder material andsaid second solder material.
 9. The electrical structure of claim 6,further comprising: a first layer of underfill encapsulant surroundingsaid first non-solder metallic core and in contact with said firstsubstrate; and a second layer of underfill encapsulant surrounding saidsecond non-solder metallic core and in contact with said secondsubstrate, wherein said first layer comprises a first coefficient ofthermal expansion, wherein said second layer comprises a secondcoefficient of thermal expansion, and wherein said first coefficient ofthermal expansion differs from said second coefficient of thermalexpansion.
 10. The electrical structure of claim 9, wherein said firstsubstrate is a semiconductor device, wherein said second substrate is achip carrier, and wherein said first coefficient of thermal expansion isless than said second coefficient of thermal expansion.
 11. Theelectrical structure of claim 1, further comprising: a solderinterconnect structure consisting of solder, wherein said firstsubstrate comprises a third electrically conductive pad, wherein saidsecond substrate comprises a fourth electrically conductive pad, andwherein said solder interconnect structure electrically and mechanicallyconnects said third electrically conductive pad to said fourthelectrically conductive pad.
 12. The electrical structure of claim 1,further comprising: a first layer of wafer level underfill encapsulantsurrounding said first non-solder metallic core and filling a spacebetween said first substrate and said second substrate.
 13. Anelectrical structure comprising: a first substrate comprising a firstelectrically conductive pad; a second substrate comprising a secondelectrically conductive pad; and an interconnect structure electricallyand mechanically connecting said first electrically conductive pad tosaid second electrically conductive pad, wherein said interconnectstructure comprises a non-solder metallic core structure and a layer ofsolder covering an entire exterior surface of said non-solder metalliccore structure, wherein said entire exterior surface completelysurrounds said first metallic structure, wherein said layer of solder isin direct electrical and mechanical contact with said entire surface ofsaid non-solder metallic core structure, and wherein said layer ofsolder electrically and mechanically connects said non-solder metalliccore structure to said first electrically conductive pad and said secondelectrically conductive pad.
 14. The electrical structure of claim 13,wherein said non-solder metallic core structure comprises a cylindricalshape.
 15. The electrical structure of claim 13, wherein said non-soldermetallic core structure comprises a spherical shape.
 16. The electricalstructure of claim 13, wherein said non-solder metallic core structurecomprises a metallic material selected from the group consisting ofcopper, nickel, and gold.
 17. The electrical structure of claim 13,wherein said non-solder metallic core structure comprises a firstmetallic structure and a second metallic structure covering and indirect mechanical contact with an entire exterior surface of said firstmetallic structure, wherein said entire exterior surface of said firstmetallic structure completely surrounds said first metallic structure,wherein said first metallic structure consists of a first metallicmaterial, and wherein said second metallic structure consists of asecond metallic material that differs from the first metallic material.18. The electrical structure of claim 13, further comprising: a solderinterconnect structure consisting of solder, wherein said firstsubstrate comprises a third electrically conductive pad, wherein saidsecond substrate comprises a fourth electrically conductive pad, andwherein said solder interconnect structure electrically and mechanicallyconnects said third electrically conductive pad to said fourthelectrically conductive pad.
 19. The electrical structure of claim 13,further comprising: a first layer of wafer level underfill encapsulantsurrounding said interconnect structure and filling a space between saidfirst substrate and said second substrate.
 20. A method for forming anelectrical structure comprising: providing a first substrate comprisinga first electrically conductive pad, a second substrate comprising asecond electrically conductive pad, and a transfer film comprising anon-solder metallic core structure, wherein said non-solder metalliccore structure comprises a cylindrical shape; forming a first solderstructure on said first electrically conductive pad; first positioningafter said forming said first solder structure, said transfer film suchthat a first side of said non-solder metallic core structure is incontact with said first solder structure; first heating after said firstpositioning, said non-solder metallic core structure to a temperaturesufficient to cause said first solder structure to melt and form anelectrical and mechanical connection between said first side of saidnon-solder metallic core structure and said first electricallyconductive pad; removing after said first heating, said transfer filmfrom said non-solder metallic core structure; forming a second solderstructure on said second electrically conductive pad; secondpositioning, after said forming said second solder structure, said firstsubstrate comprising said non-solder metallic core structure such that asecond side of said non-solder metallic core structure is in contactsaid second solder structure; and second heating after said secondpositioning, said non-solder metallic core structure to a temperaturesufficient to cause said second solder structure solder to melt and forman electrical and mechanical connection between said second side of saidnon-solder metallic core structure and said second electricallyconductive pad resulting in an electrical and mechanical connectionbetween said first electrically conductive pad and said secondelectrically conductive pad.
 21. The method of claim 20, wherein saidforming said first solder structure comprises applying a first portionof molten solder to said first electrically conductive pad from atransfer substrate comprising a first cavity filled with said firstportion of molten solder, and wherein said forming said second solderstructure comprises applying a second portion of molten solder to saidsecond electrically conductive pad from said transfer substratecomprising a second cavity filled with said second portion of moltensolder.
 22. The method of claim 20, wherein said removing said transferfilm from said non-solder metallic core structure comprises laserablating the transfer film, resulting in releasing said non-soldermetallic core structure from said transfer film
 23. The method of claim20, wherein said transfer film is bonded to said non-solder metalliccore structure with a thermally degradable adhesive.
 24. The method ofclaim 20, further comprising: after said removing said transfer filmfrom said non-solder metallic core structure, applying a wafer levelunderfill encapsulant layer to said first substrate.
 25. A method forforming an electrical structure comprising: providing a first substratecomprising a first electrically conductive pad, a second substratecomprising a second electrically conductive pad, a first transfersubstrate comprising a first cavity, and a non-solder metallic corestructure comprising a spherical shape, wherein said non-solder metalliccore structure comprises a diameter that is less than a diameter of saidfirst cavity; forming a first solder structure on said firstelectrically conductive pad; dispensing said non-solder metallic corestructure into said first cavity within said first transfer substrate;first positioning after said dispensing, said first transfer substratesuch that a first section of a surface of said non-solder metallic corestructure is in contact with said first solder structure; first heatingafter said first positioning, said non-solder metallic core structure toa temperature sufficient to cause said first solder structure to meltand form an electrical and mechanical connection between said firstsection of said surface of said non-solder metallic core structure andsaid first electrically conductive pad; removing after said firstheating, said first transfer substrate from said non-solder metalliccore structure; forming a second solder structure on said secondelectrically conductive pad; second positioning said first substratecomprising said non-solder metallic core structure such that a secondsection of said surface of said non-solder metallic core structure is incontact with said second solder structure; and second heating after saidsecond positioning, said non-solder metallic core structure to atemperature sufficient to cause said second solder structure solder tomelt and form an electrical and mechanical connection between saidsecond section of said surface of said non-solder metallic corestructure and said second electrically conductive pad resulting in anelectrical and mechanical connection between said first electricallyconductive pad and said second electrically conductive pad.
 26. Themethod of claim 25, wherein said forming said first solder structurecomprises applying a first portion of molten solder to said firstelectrically conductive pad from a second transfer substrate comprisinga second cavity filled with said first portion of molten solder, andwherein said forming said second solder structure comprises applying asecond portion of molten solder to said second electrically conductivepad from said second transfer substrate comprising a third cavity filledwith said second portion of molten solder.
 27. The method of claim 25,wherein said dispensing said non-solder metallic core structure intosaid first cavity within said first transfer substrate comprisesdispersing said non-solder metallic core structure into a liquid medium,and wherein said liquid medium comprises a liquid selected from thegroup consisting of a fluxing agent, water, alcohol, and a thermallydegradable soluble polymeric adhesive.
 28. The method of claim 25,wherein said first positioning and said second positioning comprisesusing a gaseous fluxing agent to assist in a solder wetting process. 29.The method of claim 25, further comprising: after said removing saidtransfer substrate from said non-solder metallic core structure,applying a wafer level underfill encapsulant layer to said firstsubstrate.
 30. A method for forming an electrical structure comprising:providing a first substrate comprising a first electrically conductivepad, a second substrate comprising a second electrically conductive pad,a first transfer substrate comprising a first cavity, a first non-soldermetallic core structure comprising a spherical shape, and a secondnon-solder metallic core structure comprising a spherical shape, whereinsaid first non-solder metallic core structure comprises a diameter thatis less than a diameter of said first cavity, and wherein said secondnon-solder metallic core structure comprises a diameter that is lessthan a diameter of said first cavity; forming a first solder structureon said first electrically conductive pad; first dispensing said firstnon-solder metallic core structure into said first cavity within saidfirst transfer substrate; first positioning after said first dispensing,said first transfer substrate such that a first section of a surface ofsaid first non-solder metallic core structure is in contact with saidfirst solder structure; first heating after said first positioning, saidfirst non-solder metallic core structure to a temperature sufficient tocause said first solder structure to melt and form an electrical andmechanical connection between said first section of said surface of saidfirst non-solder metallic core structure and said first electricallyconductive pad; removing after said first heating, said first transfersubstrate from said non-solder metallic core structure; applying a firstunderfill encapsulant layer to said first substrate; forming a secondsolder structure on a second section of said surface of said firstnon-solder metallic core structure; second dispensing said secondnon-solder metallic core structure into said first cavity within saidfirst transfer substrate; second positioning after said seconddispensing, said first transfer substrate such that a first section of asurface of said second non-solder metallic core structure is in contactwith said second solder structure; second heating after said secondpositioning, said second non-solder metallic core structure to atemperature sufficient to cause said second solder structure to melt andform an electrical and mechanical connection between said second sectionof said surface of said first non-solder metallic core structure andsaid first section of said surface of said second non-solder metalliccore structure; removing after said second heating, said first transfersubstrate from said second non-solder metallic core structure; forming athird solder structure on said second electrically conductive pad; thirdpositioning said first substrate comprising said first non-soldermetallic core and said second non-solder metallic core structure suchthat a second section of said surface of said second non-solder metalliccore structure is in contact with said third solder structure; and thirdheating after said third positioning, said second non-solder metalliccore structure to a temperature sufficient to cause said second solderstructure solder to melt and form an electrical and mechanicalconnection between said second section of said surface of said secondnon-solder metallic core structure and said second electricallyconductive pad resulting in an electrical and mechanical connectionbetween said first electrically conductive pad and said secondelectrically conductive pad.
 31. The method of claim 30 wherein saidforming said first solder structure comprises applying a first portionof molten solder to said first electrically conductive pad from a secondtransfer substrate comprising a second cavity filled with said firstportion of molten solder, wherein said forming said second solderstructure comprises applying a second portion of molten solder to saidsecond section of said surface of said first non-solder metallic corestructure from said second transfer substrate comprising a third cavityfilled with said second portion of molten solder, and wherein saidforming said third solder structure comprises applying a third portionof molten solder to said second electrically conductive pad from saidsecond transfer substrate comprising a fourth cavity filled with saidthird portion of molten solder.
 32. The method of claim 30, wherein saiddispensing said first non-solder metallic core structure into said firstcavity within said first transfer substrate comprises dispersing saidfirst non-solder metallic core structure into a first liquid medium,wherein said dispensing said second non-solder metallic core structureinto said first cavity within said first transfer substrate comprisesdispersing said second non-solder metallic core structure into a secondliquid medium, and wherein said first liquid medium and said secondliquid medium each comprise a liquid selected from the group consistingof a fluxing agent, water, alcohol, and a thermally degradable solublepolymeric adhesive.
 33. The method of claim 30, wherein said firstpositioning, said second positioning, and said third positioningcomprises using a gaseous fluxing agent to assist in a solder wettingprocess.
 34. The method of claim 30, further comprising: after saidremoving said first transfer substrate from said second non-soldermetallic core structure, applying a second underfill encapsulant layerto said first underfill encapsulant layer.
 35. The method of claim 30wherein said first underfill encapsulant layer comprises a material thatdiffers from a material comprised by said second underfill encapsulantlayer.
 36. The method of claim 30, wherein said first underfillencapsulant layer comprises a first coefficient of thermal expansion,wherein said second underfill encapsulant layer comprises a secondcoefficient of thermal expansion, and wherein said second coefficient ofthermal expansion is greater than said first coefficient of thermalexpansion.
 37. A method for forming an electrical structure comprising:providing a first substrate comprising a first electrically conductivepad and a second electrically conductive pad, a second substratecomprising third electrically conductive pad and a fourth electricallyconductive pad, a first transfer substrate comprising a first cavity anda second cavity, and a non-solder metallic core structure comprising aspherical shape, wherein said non-solder metallic core structurecomprises a diameter that is less than a diameter of said first cavity;forming a first solder structure on said first electrically conductivepad; forming a second solder structure on said second electricallyconductive pad; covering said second cavity with a film having anopening corresponding to said first cavity; dispensing said non-soldermetallic core structure into said first cavity within said firsttransfer substrate; first positioning said first transfer substrate suchthat a first section of a surface of said non-solder metallic corestructure is in contact with said first solder structure and said secondcavity is aligned with said second solder structure; first heating saidnon-solder metallic core structure to a temperature sufficient to causesaid first solder structure to melt and form an electrical andmechanical connection between said first section of said surface of saidnon-solder metallic core structure and said first electricallyconductive pad; removing said first transfer substrate from saidnon-solder metallic core structure; forming a third solder structure onsaid third electrically conductive pad; forming a fourth solderstructure on said fourth electrically conductive pad; second positioningsaid first substrate comprising said non-solder metallic core structuresuch that a second section of said surface of said non-solder metalliccore structure is in contact with said third solder structure and saidsecond solder structure is in contact with said fourth solder structure;second heating said non-solder metallic core structure to a temperaturesufficient to cause said third solder structure solder to melt and forman electrical and mechanical connection between said second section ofsaid surface of said non-solder metallic core structure and said thirdelectrically conductive pad resulting in an electrical and mechanicalconnection between said first electrically conductive pad and said thirdelectrically conductive pad; and third heating said second solderstructure and said fourth solder structure to a temperature sufficientto cause said second solder structure and said fourth solder structureto melt and form an electrical and mechanical connection between saidsecond solder structure and said fourth solder structure resulting in anelectrical and mechanical connection between said second electricallyconductive pad and said fourth electrically conductive pad, wherein saidsecond heating and said third heating are performed simultaneously. 38.The method of claim 37, wherein said forming said first solder structurecomprises applying a first portion of molten solder to said firstelectrically conductive pad from a second transfer substrate comprisinga third cavity filled with said first portion of molten solder, whereinsaid forming said second solder structure comprises applying a secondportion of molten solder to said second electrically conductive pad fromsaid second transfer substrate comprising a fourth cavity filled withsaid second portion of molten solder, wherein said forming said thirdsolder structure comprises applying a third portion of molten solder tosaid third electrically conductive pad from a third transfer substratecomprising a fifth cavity filled with said third portion of moltensolder, and wherein said forming said fourth solder structure comprisesapplying a fourth portion of molten solder to said fourth electricallyconductive pad from said third transfer substrate comprising a sixthcavity filled with said fourth portion of molten solder.
 39. The methodof claim 37, wherein said dispensing said non-solder metallic corestructure into said first cavity within said first transfer substratecomprises dispersing said non-solder metallic core structure into aliquid medium, and wherein said liquid medium comprises a liquidselected from the group consisting of a fluxing agent, water, alcohol,and a thermally degradable soluble polymeric adhesive.
 40. The method ofclaim 36, wherein said first positioning and said second positioningcomprises using a gaseous fluxing agent to assist in a solder wettingprocess.